1. Field of the Invention
The invention relates to a method for purifying water, the water which is to be cleaned and which contains organic and/or inorganic particles being conveyed into a filtration plant containing filler material, being purified as a result of forming a trickling stream and subsequently being removed through at least one outlet, and to an apparatus for carrying out the method.
2. Description of the Prior Art
The above-mentioned method and the device working according to this method are well known in practice in connection with so-called trickle filter plants. In such plants, the water to be purified/filtered is guided over an arrangement of trickle elements. Bacteria, which filter protein and other organic compounds out of the water and decompose these by means of specific metabolic processes, settle on the trickle elements. On this way, the water passes over the trickle elements very slowly so that a bacterial purification of the water may take place in to an adequate extent. In other words, one can talk rather of trickling than of flowing, let alone of pouring. A disadvantage of this method is that, as the water can be sent through the filtration arrangement only very slowly, a correspondingly large dimensioning of the arrangement is necessary or an increased water throughput must be carried out with a smaller dimensioning of the plant in a closed water circuit, in order to obtain an adequate purification result. In addition, the purification of the water is based only on the bacterial decomposition of organic substances. Apart from the gases which are set free inorganic and also organic substances remain in the water, which, in closed water circuits, possibly leads to an accumulation of toxicants; hence, a frequent exchange of the water in fresh water aquaristic is normally unavoidable. Furthermore it is disadvantageous that due to the required slow trickling velocities, the evaporation of the water is very high, possibly resulting in a concentration of salt in the water. A trickle filter plant also requires an initialization period of several weeks before the device can be used fully to allow the bacteria to settle or the trickle elements. Finally, very high amounts of oxygen are required by the bacteria for the bacterial decomposition of organic substances, the oxygen being extracted from the water itself. Additional energy is required for the supply of oxygen. Finally, the discharged water can be polluted with the excrements and metabolic products of the bacteria.
A further problem of fresh water plants such as e.g. nutrition rich ponds, is that the formation of algae caused by insolation leads to considerable fluctuations in the pH level and impedes vision.
DD 241 406 discloses a trickle film reactor without a valve tray for the continuous elimination from water which is essentially free of suspended matter of substances dissolved in the water, the reactor being filled with fine-grain filler material having a density of essentially less than 1 g/cm.sup.3 and having a banking-up height control device. A reactor of this kind is likewise limited in its flowing velocity, as the purification of the water occurs bacterially. Furthermore, the reactor is not suitable for water containing larger amounts of suspended matter, as this might clog the small filler material particles causing blockage of the reactor.
Furthermore, a method for the purification of salt water from contamination by proteins and other organic compounds has been known since the beginning of the 1070s, the method exploiting the ability of protein and the other organic substances to form foam. The water (sea water) containing high amounts of sodium chloride is set in motion by supplying air from below, causing the proteins to be pulled with the upwardly bubbling air and resulting in a strong foam formation on the surface. The foam which then accumulates on the surface can be skimmed off, the nitrogen containing organic compounds being simultaneously removed. The water inlet of such a plant is located below the surface of the water, so that the salt water flowing in does not come into contact with the formed foam layer. Plants of this kind are suited only for salt water aquariums, in which the filtration occurs via a filtration column, so that the water having a high sodium chloride content is continuously exchanged through inlet and outlet. This method cannot be applied to fresh water as fresh water has a higher interfacial surface tension and a lower density than water which contains sodium chloride.
A further disadvantage of this method is that the air supply also occurs from below, namely by blowing into the water, which requires energy to be expended.
Moreover, U.S. Pat. No. 4,988,436 discloses a filtration system for an aquarium having two purification steps, viz. one biological filtration step via a conventional trickle filter and one skimmer step. The water is initially guided over a trickle filter, where it is purified by bacteria. Afterwards the water is fed to a chamber in which skimming takes place by means of air blown into the water from below, i.e. against the direction of flow of the water. A foam layer, in which the impurities are deposited, forms on the surface of the water in the chamber.
A disadvantage of this method is that here,.too, the flow velocity of the water and consequently the water throughput of the arrangement depend on the purification via the trickle filter. For an effective biological purification, the water must be sent over the trickle filter very slowly. In addition, energy is required for blowing in the air in the second purification step, because the air is blown against the downwardly flowing water.